Tropical Storm GREG

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TROPICAL STORM GREG DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL EP072011
800 AM PDT WED AUG 17 2011
SATELLITE IMAGERY INDICATES THAT GREG HAS STRENGTHENED THIS MORNING
AS A CENTRAL DENSE OVERCAST HAS DEVELOPED WITH AN OUTER CONVECTIVE
BAND OVER THE NORTHWESTERN SEMICIRCLE. SATELLITE INTENSITY
ESTIMATES ARE 55 KT FROM TAFB AND 35 KT FROM SAB...SO THE INITIAL
INTENSITY IS INCREASED TO 45 KT. ANALYSES FROM CIMSS AT THE
UNIVERSITY OF WISCONSIN SHOW 10-15 KT OF NORTHEASTERLY VERTICAL
WIND SHEAR STILL AFFECTING THE STORM...AND RECENT MICROWAVE DATA
SUPPORTS THIS BY SHOWING A SOMEWHAT SHEARED PATTERN TO THE
CONVECTION UNDERNEATH THE CDO.
THE INITIAL MOTION IS NOW 300/18...WHICH IS FASTER THAN BEFORE.
GREG IS LOCATED BETWEEN A LARGE MID/UPPER-LEVEL RIDGE OVER THE
SOUTHERN UNITED STATES AND NORTHERN MEXICO AND A LARGE BUT WEAK
TROPICAL DISTURBANCE TO ITS WEST AND SOUTHWEST. DURING THE NEXT
COUPLE OF DAYS...THE DISTURBANCE IS FORECAST TO WEAKEN DUE TO ITS
PROXIMITY TO GREG...LEAVING THE RIDGE TO THE NORTH AS THE MAIN
STEERING MECHANISM. THIS EVOLUTION SHOULD STEER THE STORM QUICKLY
TOWARD THE WEST-NORTHWEST FOR 24 HR OR SO...FOLLOWED BY A GRADUAL
TURN TOWARD THE WEST AND A DECREASE IN FORWARD SPEED. THE TRACK
GUIDANCE FOLLOWS THIS SCENARIO...ALTHOUGH THERE HAS BEEN A
NORTHWARD SHIFT LIKELY DUE TO THE INITIAL POSITION AND MOTION. THE
NEW FORECAST TRACK IS FASTER THAN AND A LITTLE TO THE NORTH OF THE
PREVIOUS FORECAST...AND IT LIES CLOSE TO THE VARIOUS CONSENSUS
MODELS.
THE FORECAST TRAVCK KEEPS GREG OVER SEA SURFACE TEMPERATURES OF 27C
OR WARMER FOR 36 HR...AND THE DYNAMICAL MODELS FORECAST THE SHEAR
TO DECREASE DURING THIS TIME. THIS COMBINATION SHOULD ALLOW
CONTINUED STRENGTHENING...AND THE NEW INTENSITY FORECAST CALLS FOR
A PEAK INTENSITY OF 75 KT IN 36 HR AS A BLEND BETWEEN THE SHIPS AND
LGEM MODELS. AFTER 48 HR...THE WATERS GET COOLER ON THE FORECAST
TRACK...WHICH SHOULD INDUCE A STEADY WEAKENING TREND.
FORECAST POSITIONS AND MAX WINDS
INIT 17/1500Z 16.7N 104.2W 45 KT 50 MPH
12H 18/0000Z 17.7N 106.6W 55 KT 65 MPH
24H 18/1200Z 18.4N 109.4W 65 KT 75 MPH
36H 19/0000Z 19.0N 111.8W 75 KT 85 MPH
48H 19/1200Z 19.4N 113.6W 75 KT 85 MPH
72H 20/1200Z 20.0N 116.5W 65 KT 75 MPH
96H 21/1200Z 20.5N 119.0W 45 KT 50 MPH
120H 22/1200Z 20.5N 122.0W 30 KT 35 MPH
$$
FORECASTER BEVEN
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